In recent years, apparatuses that compress images by implementing an encoding method for compressing image information through orthogonal transforms such as discrete cosine transforms and motion compensation by using redundancy inherent to image information, have been spreading so as to handle image information as digital information and achieve high-efficiency information transmission and accumulation in doing do. This encoding method may be MPEG (Moving Picture Experts Group), for example.
Particularly, MPEG2 (ISO/IEC 13818-2) is defined as a general-purpose image encoding standard, and is applicable to interlaced images and non-interlaced images, and to standard-resolution images and high-definition images. MPEG2 is currently used in a wide range of applications for professionals and general consumers, for example. By using the MPEG2 compression method, a bit rate of 4 to 8 Mbps is assigned to a standard-resolution interlaced image having 720×480 pixels, for example. Also, by using the MPEG2 compression method, a bit rate of 18 to 22 Mbps is assigned to a high-resolution interlaced image having 1920×1088 pixels, for example. In this manner, a high compression rate and excellent image quality can be realized.
MPEG2 is designed mainly for high-quality image encoding suited for broadcasting, but is not compatible with lower bit rates than MPEG1 or encoding methods involving higher compression rates. As mobile terminals are becoming popular, the demand for such encoding methods is expected to increase in the future, and to meet the demand, the MPEG4 encoding method was standardized. As for an image encoding method, the ISO/IEC 14496-2 standard was approved as an international standard in December 1998.
On the standardization schedule, the standard was approved as an international standard under the name of H.264 and MPEG-4 Part 10 (Advanced Video Coding, hereinafter referred to as H. AVC) in March 2003.
As an extension of H.264/AVC, FRExt (Fidelity Range Extension) was standardized in February 2005. FRExt includes coding tools for business use, such as RGB, 4:2:2, and 4:4:4, and the 8×8 DCT and quantization matrix specified in MPEG-2. As a result, an encoding method for enabling excellent presentation of movies containing film noise was realized by using H.264/AVC, and the encoding method is now used in a wide range of applications such as Blu-ray Disc (a trade name).
However, there is an increasing demand for encoding at a higher compression rate so as to compress images having a resolution of about 4000×2000 pixels, which is four times higher than the high-definition image resolution, or distribute high-definition images in today's circumstances where transmission capacities are limited as in the Internet. Therefore, studies on improvement in encoding efficiency is still continued by VCEG (Video Coding Expert Group) under ITU-T.
At present, to achieve higher encoding efficiency than that of H.264/AVC, an encoding method called HEVC (High Efficiency Video Coding) is being developed as a standard by JCTVC (Joint Collaboration Team—Video Coding), which is a joint standards organization of ITU-T and ISO/IEC. As of April 2011, Non-Patent Document 1 related to HEVC has been issued as a draft.